1). Field of the Invention
The present invention is concerned with light sources and more particularly with light sources which utilise a set of light emitters arranged in an array.
2). Discussion of Related Art
Light emitting diodes (LEDs) are often used in this manner. The intensity of a single LED is, despite recent developments in high intensity LEDs, typically smaller than that of a conventional tungsten filament bulb or halogen bulb. To provide increased light intensity from an LED source it is thus known to arrange a set of LEDs side by side in an array, e.g. on a carrier such as a printed circuit board. In this way LED bulbs have been constructed which can be substituted for conventional incandescent bulbs, as to which see for example U.S. Pat. No. 4,211,955 (Ray).
A problem can arise in some contexts due to the lateral dimensions of such an array, as FIGS. 1 and 2 will make clear. FIG. 1 shows a conventional incandescent bulb 2 arranged to emit through a limited aperture 4. The actual light emitting element of the bulb—its filament—has small depth 6 which is in this example not as large as the depth of the aperture 4. As a result a large proportion of the bulb's output can be directed through the aperture, as desired. Compare this with FIG. 2, in which an array 8 of LEDs 9 has been substituted for the bulb 2. Because of its use of multiple LEDs, the array 8 has a depth 10 greater than the width of the aperture 4 and as a result part of the array is obscured.
This type of problem can in particular arise where a light source using a multiple array of light emitters is substituted for a conventional bulb. It is not limited to situations in which light must pass through an aperture. Various optical or packaging requirements can necessitate provision of a light source whose effective depth—i.e. the depth of the emitted beam—is relatively small. To make it possible to provide such a light source while using an array of light emitting elements is an object of the present invention.
An additional or alternative object of the present invention is to provide a light source, using an array of light emitters, which has small depth measured transverse to the direction of an emitted beam.
In the FIG. 2 example, an obvious solution might be to use a conventional circular lens between the array 10 and the aperture 4. Such a solution may not be practical in all cases, particularly due to packaging requirements. It is particularly desired to overcome the above described problems using a light source which is compact.